Fixed two more cases of outdated shared memory cache detection

Fixed two more cases of outdated shared memory cache detection
which led to "STORE_DISK_CLIENT == getType()" assertions
when running SMP Squid with non-shared memory caching.

UsingSmp() is not the right condition to detect whether we are using a shared
memory cache because shared memory caching may be disabled and because
Coordinator does not use a shared memory cache even if shared caching is
enabled.

See also: r11821.